A valve timing adjusting system includes a displacement mechanism unit that displaces a camshaft rotational phase relative to a crankshaft, a locking mechanism unit that locks the rotational phase, and a control unit that controls operations of a hydraulic control valve. The control unit includes a property obtainment unit that obtains property information regarding hydraulic properties, and a lock release process completes locking release by supplying oil pressure to the locking mechanism unit for moving the rotational phase from an intermediate locked phase toward one of a retard/advance position, and then supplying oil pressure to the locking mechanism unit for moving the rotational phase toward the other of the retard/advance position; the rotational phase stands by at a predetermined position of the one of the retard/advance position past the intermediate locked phase during the lock release process, until a standby time has elapsed.